Progress on IE syntax?

Szeremenyi, in his "Introduction to Indo-European Linguistics", writes that
syntax is one of the most uncertain and contentious areas of IE study.
Lehmann, however, asserts in his "Theoretical Bases of Indo-European
Linguistics" that syntax has been essentially figured out and there's nothing
left to uncover. So, I ask a linguist experienced in this to let me know what
to believe.

I'd also be grateful for any opinions on the Lehmann book. He seems quite sure
of himself and sets as unarguable fact matters that are portrayed as more
uncertain in other works.

Christopher Culver